This invention relates to DC power supply devices, and, in particular, to devices which can supply a plurality of different DC powers with regulated voltages to operate a plurality of different loads.
Electronic parts and instruments are operated by DC powers and it is necessary to feed the DC power with a stable voltage level for the stable operation of such instruments and parts with high reliability.
Various DC regulator circuits such as, so called, series regulators, switching regulators, magnetic amplifier regulators and others have been known and used in the prior art to supply regulated DC voltage.
Furthermore, to develop a different voltage DC power from a given DC power, a DC-DC converter has been known and used in the prior art. The DC-DC converter usually comprises a DC-AC inverter circuit including an inverter transformer and a rectifier circuit. The DC-AC inverter circuit is classified into a self-exciting type and a separately-exciting type in the prior art.
To obtain a desired regulated voltage DC power from a DC power source, a DC-DC converter and a voltage regulator are used in combination.
Transistor circuits and/or integrated circuits are used in the DC-DC converter and the voltage regulator to make the regulated voltage DC power supply circuit small in size with a high efficiency and a low power loss.
On the other hand, a plurality of electronic instruments are often operated at one time. In such a case, DC-DC converters and voltage regulators are required correspondingly to respective instruments. But this results in increase of the volume of the entire system.
Therefore, in a certain case a single DC-AC inverter circuit is used which includes an inverter transformer having a plurality of secondary windings, to each of which windings a rectifier circuit and a regulator circuit are connected.
In this arrangement, if series regulator circuits are used, a greater heat radiation fin or a cooling device is required because voltage variation of a DC power source is applied to the regulator circuits to increase the heat developed at transistors in the circuits. Thus this arrangement fails in the reduction of the volume of the entire system.
If switching regulator circuits are used, series regulator circuits must be used in cascade, or a resistor must be used in series, to minimize the output ripple voltage at smaller loads. Therefore, in case regulated voltage DC powers are fed to smaller loads, this arrangement fails in the reduction of the volume.